Biological labels such as fluorescent dyes are widely used in biological research and medical diagnostics. Fluorescent dyes are superior to conventional radioactive materials because fluorescent dyes are less expensive and less toxic, and can typically be detected with sufficient sensitivity. Indeed, a diversity of fluorophores with a distinguishable color range has made it more practical to perform multiplexed assays capable of simultaneous detection of multiple biological targets. The ability to visualize multiple targets in parallel is often required for delineating the spatial and temporal relationships amongst different biological targets in vitro and in vivo. In addition, the generation of a wide range of fluorescent dyes has opened a new avenue for conducting high-throughput and automated assays, thus dramatically reducing the unit cost per assay. Moreover, the low toxicity of fluorescent dyes provides ease of handling in vitro, and also renders it safer for imaging biological processes in vivo.
Biological labels for applications described above are often prepared by conjugating a reactive label, such as a reactive dye, to a protein that is capable of binding to a given target or binding partner. The purity of the protein is a critical factor for such a labeling reaction to proceed efficiently. This can be difficult to achieve, particularly with proteins such as antibodies. For example, most commercial antibody products are supplied as a mixture of the antibody and a protein stabilizer such as BSA or gelatin. Moreover, some antibodies are supplied in relatively crude forms, such as ascites fluids and hybridoma cell supernatant, which contain many components besides the antibody. It has been reported that such components can interfere with the labeling reaction and therefore render the results unsatisfactory.
Conventional processes for conjugating dyes to protein binding agents such as antibodies typically require purification of the antibody away from other buffer components, including stabilizers, prior to the conjugation reaction. Purification of the labeled antibody may also have to be performed once the reaction is complete. Purification steps are generally undesirable because preparations of antibody available to a user may contain a very low amount of antibody, and purification may result in loss of valuable antibody. As such, conventional antibody labeling technique is tedious and time consuming.